High vacuum getter



May 10, 1949. J. BEERS I 2,469,626

HIGH VACUUM GETTER Filed June 20, 1946 INVENTOR JOHN /P. EE'RD BYATTORNEY.

Patented May 10, 1949 HIGH VACUUM GETTER John R. Beers, BriarcliflManor, N. Y., assignor, by mesne assignments, to Philips Laboratories,Inc., Irvington on Hudson, N. Y., a corporation of Delaware ApplicationJune 20, 1946, Serial No. 678,120

8 Claims. 1

My invention relates to electron discharge tubes and more particularlyto a getter means capable of maintaining a high degree of vacuum in suchtubes.

Cathode ray tubes employing magnetic beam deflection generally sufierfrom the disadvantage that in operation they develop a so called ionspot. This ion spot has been found to be chiefly due to the presence ofminute quantities of gas. Notwithstanding careful evacuation and agingof the tube, it has been diflicult to evacuate it to the extent that thegas is reduced to an amount below that at which ion spots occur, and insome instances it has been necessary to employ an ion trap in the tubewhereby the ions formed are directed towards portions of the tube otherthan the fluorescent screen.

It is an object of my invention to provide a novel structure for vacuumtubes whereby gas retained after evacuation is substantially completelyabsorbed.

Another object of my invention is to provide a novel structure forcathode ray tubes whereby the gas remaining after evacuation issubstantially completely absorbed, thereby precluding the necesslty foran ion trap in tubes which are to be operated with magnetic deflection.

A further object of my invention is to provide a getter for absorbinggas which getter is eifective throughout the life of the vacuum tube.

These and further objects of the invention will appear as thespecification progresses.

In accordance with the invention, these objects are achieved by means ofa novel getter arrangement. I have found that at temperatures in theregion of 400 C. zirconium readily absorbs hydrogen forming a solidsolution of the gas in the metal. At still higher temperatures,zirconium absorbs other gases, and may release some hydrogen absorbed atlower temperatures. For example, increasing the temperature toapproximately 1000 C. causes the zirconium to release some of thehydrogen previously absorbed while absorbing the nitrogen and oxygengases present in the atmosphere of the tube. I utilize these propertiesof zirconium most effectively in removing the residual gases in electrondischarge tubes requiring a high degree of vacuum by maintainingportions of the zirconium at different temperatures during the operationof the tube.

I- continuous zirconium getter is shown mounted within a vacuum tubeheater-cathode structure.

Referring now to the figure, a heater wire II is wound in a re-entranthelix around a cylinder l2 of a refractory insulating material such asceramic. A thin zirconium strip formed into a cylinder I3 is insertedinto cylinder I2. A stem I8 of the zirconium cylinder I3 extendsslightly below cylinder I2 and is welded to a support wire it which ismounted in the press of the base I! p of the tube. The lower end of thezirconium cylinder I3 is open to permit the residual gases in the tubeto enter the cylindrical enclosure and allow the zirconium to absorbthese gases. The heater wire II is connected to the tube electrodesthrough, lead-in wires I5 and I6 respectively. The heater structure isenclosed within a cathode structure I!) such for example, as thosecustomarily employed in cathode ray tubes having its upper end I 0coated with an electron emissive substance, as shown. The evacuatedenvelope 20, which may be made of glass or the like and within which thecathode assembly and other elements are enclosed, is shown broken awaynear the base 2| of the tube. The remaining structure of the tube is notshown as it is not necessary for an understanding of the invention.

If a portion of the zirconium is exposed directly to the heater II, Ihave found that some of the zirconium may contact or be evaporated ontothe heater element, particularly during processing, with deleterious'efi'ects. Therefore, I have afforded complete protection andseparationof the zirconium from the heater wire by not only surrounding thezirconium cylinder I3 with a cylinder I2 of refractory insulatingmaterial, but also by sealing the top of the cylinder I2 with a sealingmaterial such as ceramic cement.

The zirconium is heated to a temperature in the the the base thereof isoperating at normal tube In order that the invention may be more clearlyunderstood and readily carried into effect, it will now be describedwith reference to the accompanying drawing in which the sole figureshows a preferred embodiment of my invention wherein a temperature. Thetemperature gradient thus afforded offers a unique advantage in that thelower surface of the zirconium absorbs and retains the hydrogen in theatmosphere of the tube while the upper surface absorbs other gases suchas nitrogen and oxygen. I have found that exposure of a portion of thezirconium below the ceramic cylinder I2, and thus out of the heaterstructure, is a particularly advantageous and emcient means foraffording a continuous temperature gradient along the zirconium. Theexposed portion may be flattened as shown, to permit easy connection,for example, by welding to a support of metal on the inner surface ofcylinder l2. In

the latter form, a substantial thickness of metal. say several micronsthick, is desirable in order that the zirconium may function effectivelyto clean up the residual atmosphere in the tube,

It will be understood that the term cylinder as used in thespecification may include other than circular cylinders. Likewise,various other shapes, such as a rod, a corrugated strip, or a ribbon ofzirconium may be employed supported within a cylinder of refractoryinsulating material, particularly if space is allowed for the residualgases in the tube to have access to the zirconium.

While I have described my invention with specific examples andapplications, other variations will suggest themselves to those skilledin the art without departing from the spirit and- I refractoryinsulating member having at least two surface portions in heat exchangerelationship, electrical heating means adjacent to one said surfaceportion of said member for heating the other surface to a giventemperature, and heat responsive gas absorbing means non-volatile atsaid temperature adjacent to said other surface portion.

.2. An electron discharge device comprising a tubular refractoryinsulating member having an inner surface and an outer surface in heatexchange relationship, electrical heating means adjacent to said outersurface for heating said inner surface to a given temperature, and heatresponsive gas absorbing means non-volatile at said temperature adjacentto said inner surface.

3. An electron discharge device comprising a tubular refractoryinsulating member, an electrical wire element wound on said tubularmember, and a tubular gas absorbent member responsive to heat withinsaid insulating member.

4. An electron discharge device comprising a heat responsive gasabsorbing member, means to heat said gas absorbing member non-uniformlyover the length of said member, said means comprising an electricalheating wire element surrounding a portion of said gas absorbing member,and a cathode in heat transfer relationship with said heating wireelement.

5. An electron discharge device having a cathode assembly comprising atubular zirconium member, a tubular refractory insulating membersurrounding said zirconium member, an electrical heater wire elementsurrounding a portion of said zirconium member, and a cathode in heattransfer relationship with said heating wire element.

6. An electron discharge device comprising an evacuated envelope and,within said envelope, a tubular zirconium member to absorb residual gas,a refractory insulating. tubular member surrounding a portion of saidzirconium member, electrical heating means disposed around saidinsulating member, and a cathode in heat transfer relationship with saidheating means.

7. An electron discharge device comprising a tubular zirconium member, atubular refractory insulating member surrounding a portion of saidzirconium member, means to heat said zirconium member non-uniformly overthe length thereof comprising an electrical wire element surroundingsaid refractory member. and a cathode in heat transfer relationship withsaid heating wire element.

8. An electron discharge device comprising an evacuated envelope acathode structure mounted within said envelope, a refractory insulatingtubular member mounted within said cathode structure, cathode heatermeans disposed between said structure and said tubular member, and atubular zirconium member disposed within said refractory member, aportion of said zirconium member extending out of said refractorymember.

JOHN R. BEERS.

REFERENCES CITED UNITED STATES PATENTS Number Name I Date McQuade Nov.21, 1939

